Food, fertilizers and our nitrogen footprints

Volume 11 Number 2 February 9 - March 8 2015

 

Daryl Holland speaks to researchers about how the food we eat leaves a nitrogen footprint behind back on the farm.

No doubt you have heard of a carbon footprint. But what do you know about your nitrogen footprint?

Nitrogen fertilisers are a major contributor to greenhouse gas emissions and other forms of pollution, yet when we go to the supermarket we have no way of knowing how much nitrogen was used to make the products we buy.

Professor Deli Chen, Dr Helen Suter and their colleagues in the soils group want to change that.

“We want to develop a scientific index, which is called a nitrogen footprint,” Professor Chen says.

This index would let consumers know how efficiently the farmer used nitrogen fertiliser when producing their food.

He gives, as an example, the star rating system that is used on whitegoods and other electrical products.

Professor Chen believes that environmentally conscious consumers will respond to nitrogen footprint labelling and best practices in farm management that reduce this footprint will be rewarded with premium prices.

“The reality is that half of the nitrogen applied to the soil is lost to the environment,” he says.

Some of this ‘lost’ nitrogen leaches into rivers, lakes and the ocean and can cause harmful algal blooms, oceanic ‘dead zones’ and other environmental problems, while some is released into the atmosphere as various gases, including nitrous oxide (N2O), which is a major greenhouse gas.

To precisely measure nitrogen losses from soils, Professor Chen’s group is using state-of-the-art equipment such as Quantum Cascade Lasers, which can measure concentrations of N2O in the air down to 40 parts per trillion, and repeat this measurement ten times per second.

“We are the best equipped group in the world, for studying all of these gases,” Professor Chen says.

Dr Suter is leading a collaboration with fertiliser company Incitec Pivot Limited to develop what they call enhanced efficiency fertilisers.

One of the fertilisers they are testing contains a nitrogenase inhibitor that blocks the chemical reaction that turns ammonia into nitrate.

Nitrate is the substrate for a process called denitrification, which releases nitrogen gases, including N2O, into the atmosphere. Nitrate is also much more likely than ammonia to be leached out of soil and lost in the groundwater.

Dr Suter says the research is challenging and the results don’t always go as planned.

“In some cases we can find differences in soil mineral nitrogen with some of these products, and in other cases we don’t seem to pick up those differences. So that depends on the situation - the climate, how much rainfall we’ve had, how wet the soil is, and what kind of soil it is,” she says.

Key to these differences are the soil microbes that process the nitrogen and the soils group last year welcomed international soil microbe expert Professor Jim He, who joined the University through the Researcher at Melbourne Accelerator Program (R@MAP).

Professor Chen says the ultimate aim of the project is to develop “a fertiliser that can reduce losses, improve efficiency, reduce greenhouse gas emissions, and can lower the nitrogen footprint”.

On the eve of International Year of Soils, Dr Suter wants people to think more about how important the health of our soils is.

“Now, people will go to the shop and buy their steak, for example, in a piece of polystyrene and a plastic wrap and there’s a complete disconnect from where that has come from,” she says.

“So I think that’s what I’d like to see - it’s people getting a greater understanding of how important the soil is for food.”

 

www.fvas.unimelb.edu.au